The proof in a nutshell is this: "If I am seriously trying to understand
fully the world I live in, then I am already convinced that God exists."
The peculiar force and power of the proof is exactly the force and power
of the concrete judgment of fact underlying it; namely, the judgment
achieved
in Chapter 11: "I am a knower." Chapter 11 of Insight was focused
on bringing the reader to make that concrete judgment of fact in the awareness
that he or she could not reasonably help making it and could never reasonably
go back on it. The same will be true of the conclusion finally drawn from
it in Chapter 19.
There is, however, another side to this. Just
as "I am a knower" has no binding force for other people, who do not know
about me what I know about myself, so the same is true of a metaphysics
built on "I am a knower."

"No one can understand for another or judge for another.
Such acts are one's own and only one's own. Explicit metaphysics
is a personal attainment." --Insight, 396

"[Explicit metaphysics] can exist only in a self-affirming subject,
and the process can be produced only by the subject in which the result
is to exist. It follows that the directives of the method must be
issued by the self-affirming subject to himself" -- "Insight, 398.

What Lonergan writes about explicit metaphysics is true about affirming
the existence of God: "As each has to ask these questions for himself,
so each has to answer them for himself" (329).
Thus Lonergan openly makes the very focus of his
proof that which John Hick would later describe as the
hidden premise of all
arguments for the existence of God: one's own conviction that the world
is intelligible. Lonergan turns to those who claim to doubt that
premise and invites them to ask themselves why they too spend so much
time and effort trying to understand the world. His Chapter
19 is a metaproof.